JPS62189846A - Method for transmitting digital signal - Google Patents

Abstract

PURPOSE:To quicken the digital transmission by bisecting one time slot of data, giving a phase transition of plural angles in the same direction and giving an equal phase transition at each prescribed number. CONSTITUTION:One time slot of data is divided into the first half and the latter half at a prescribed ratio. Then plural kinds of phase transitions phi1-phi3 of different transitions in the same direction are given to all time slots. Further, the phase transition is made equal between time slots apart by an optional n-time slot and a signal having information transmitted to the phase difference between the first and the later halves is used as a transmission signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital signal transmission method for transmitting digital signals on a multipath transmission path such as wireless transmission in urban areas.

Conventional Technology In recent years, even in the field of mobile communications, digitization has been progressing due to improved confidentiality, more sophisticated communications, and compatibility with surrounding communication networks. However, in urban areas where such demand is thought to be most concentrated, communication quality deteriorates significantly due to multipaths caused by reflection and diffraction from buildings and other structures.

In the case of digital transmission, when the propagation delay time difference between the respective waves constituting a multipath becomes impossible to ignore with respect to the data time slot, the code error rate characteristic deteriorates significantly due to waveform distortion and poor tracking of the synchronization system.

An example of the above-mentioned conventional digital signal transmission method will be described below with reference to the drawings.

FIG. 8 shows the phase transition of a transmission signal in a conventional digital signal transmission method. T indicates one time slot of data. When the data is 1, the phase transitions by 180'', and when the data is 0, no phase transition occurs. This signal format is called differentially encoded two-phase phase modulation.

To detect such a transmission signal, for example, delay detection having a delay line of one time slot can be used.

Now, as a typical example of multipath, consider what happens to the detected output signal under two-wave multipath with a propagation delay time difference τ that is not negligible compared to the time slot.

Note that waves that are ahead in time are called direct waves, and waves that are delayed are called delayed waves.

FIG. 9 is a diagram illustrating what happens to the detected output signal when the transmission signal shown in FIG. 8 is subjected to delay detection under two-wave multipath. Figure 9(a) shows
This shows the phase transition of a direct wave. On the contrary,
The phase transition of the delayed wave delayed by the propagation delay time difference τ is
The detection output at a certain point in time is the vector inner product of the composite phase of the two waves at that time and the composite phase of the two waves l time slots ago. For example, see Figure 9 (C
), the detected output in the section B is the value of the vector inner product of the two-wave composite phase at B' and that at B.

FIG. 10 illustrates the combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point of A to C. Note that the amplitude ratio of the direct wave and the delayed wave is ρ, and the phase difference is α. From FIG. 10, the detection output at each time point A to C in FIG. 9 IC) is as follows.

A... Undefined B... 1+ρ2+2ρcosαC...
...In undefined intervals A and C, the values become undefined depending on the data values of the previous and subsequent time slots, respectively. After delayed detection, a low-pass filter is usually inserted to remove unnecessary noise components, so the final detection output signal waveform is as shown in Figure 9 (C).
The filter is applied to the solid line waveform □, resulting in a waveform as shown by the dotted line in Fig. 9, 10), which forms part of the eye pattern. By the way, when ρ is close to 1 and α is close to 180'', the detection output in the section B, which is the effective detection output, is
It becomes zero.

Therefore, the eye is closed and the bit error rate characteristics are degraded.

Also, at this time, since the invalid detection outputs in sections A and C are much larger than the effective detection output in section B, the eye fluctuates greatly in the time axis direction, making it impossible for the recovered clock to follow, and the bit error rate further increases. Significant deterioration. (For example, Onoue et al., “Code error rate characteristics 1 in Rayleigh fading with propagation delay time difference,” IEICE Technical Report, C58l-168
, 1982, or Takai et al., "Analysis of instantaneous code errors caused by multiple wave propagation and error generation mechanism based on bit synchronization system", IEICE Technical Report, C383-158, 1984) Problems to be solved by the invention However, the above-mentioned problem In such a method, the waveform distortion due to multipath is significant as described above, and the code error rate is significantly degraded. In particular, when examining the relationship between signal S/N ratio and error rate, there are regions where the error rate does not decrease even if the S/N ratio is improved. Such code errors are called irreducible errors.

Due to such so-called irreducible errors, the actual data transmission speed in urban areas is severely limited, making high-speed transmission impossible.

In view of the above-mentioned problems, the present invention provides a digital signal transmission method that allows high-speed digital transmission on multipath transmission lines in urban areas and the like.

Means for Solving the Problems In order to solve the above problems, the present invention has phase transitions of multiple types of angles between the digital portion and the second half, and the direction of the phase transitions is determined according to each time slot. are either all leading or all lagging, and are transmitted by the phase transition within any time slot and the phase difference between the first half and the second half of these two time slots, respectively, separated by that muslot. A transmission signal containing information is used as a transmission signal.

Operation The present invention uses the above-mentioned transmission signal to
When performing delayed detection, two types of effective detection outputs can be obtained for each time slot.

By combining these outputs, a type of diversity effect is achieved, which significantly improves the bit error rate under multipath conditions. Furthermore, since it is possible to obtain two types of valid detection output sets in different time slots, which differ only in the type of phase transition angle, burst errors can be reduced, error correction can be simplified, and even under multipath conditions. The bit error rate is further improved. The effects described above enable higher-speed digital transmission than in the past on multipath transmission lines.

Embodiment Hereinafter, a digital signal transmission method according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a phase transition diagram showing the phase transition of a transmission signal in the digital signal transmission method of the present invention. Transmission signals of the digital signal transmission method of the present invention will be explained below with reference to FIG.

As shown in FIG. 1, one time slot of data is divided into a first half and a second half. The time of one time slot is shown as T, the time of the first half as TI, the time of the second half as T2, and between the first half and the second half, φ1
There is always a phase transition as shown by ~φ3. The directions of these phase transitions are constant in all time slots, but there are multiple types of transition amounts depending on the time slot.

That is, in FIG. 1, the positive phase axis may be leading or lagging, and the phase transition direction is always leading or lagging. On the other hand, in this example, the phase transition amount is φ8,
There are three types indicated by φ2 and φ. Note that the number of types of phase transition amounts is three in this example, but can be arbitrarily selected.

Therefore, some values may be the same. however,
As shown in Figure 1, n time slots apart,
The amount of phase transition within both time slots must be equal. Therefore, n can be arbitrarily selected as long as it takes into account the type of phase transition amount. Of course, n is an integer of 2 or more. Further, the ratio of T1 and Tt may be set arbitrarily. Of course, T1 and T may be equal.

The phase difference between the first half of a given time slot and the first half after that n time slots, and similarly the phase difference between the second half, are equal because the phase transitions in both time slots are the same amount and in the same direction. . In FIG. 1, for example, the phase difference between the second time slot and the (n+2)th time slot is θ, as shown in the figure. Digital information is transmitted based on the value of the phase difference θ between time slots separated by n time slots. For example, if we use a two-phase system with 0° and 180° as the possible values of θ,
By assigning 0 and 1 to each, 1
Bit information is transmitted. Also, θ is 0°, 90
If a 4-phase system with angles of
8-phase system of °, 45°, 90°, etc., as well as 0°
, 22.5°, 45°, 67.5°...16
Polyphasic systems that are powers of 2, such as phase systems, that use only some of the angles above, polyphasic systems that are not powers of 2, and where the interval between the possible values of θ is constant. The value of θ may be any value as long as the value corresponds to the information to be transmitted.

As described above, the phase transition of the transmission signal in the digital signal transmission method of the present invention is T1, Tz, φ1..., θ, n
There are various values depending on the value of
An example is shown in the figure.

Figure 2 shows the phase transition of a transmission signal that transmits 1 bit of data per l time slots when n = 2, φ1 = 45°, φ2 = 135°, corresponding to θ = 0°, 180°. An example is shown.

In FIG. 3, n=2 and φ, as in the case of FIG.

=45°,φ! = 135°, θ=o', 180
” Correspondingly, an example of the phase transition of a transmission signal that transmits 1 bit of data per 1 time slot is shown. In the transmission signal of the digital signal transmission method of the present invention, the first half and The phase difference between the latter half parts, more precisely, the initial phase difference, can be freely selected. ing.

Figure 4 shows (0,0), (1, 0), (1,1)
, (0, l), which transmits two bits of data per time slot. In this case, it is also possible to use offset four-phase phase modulation in which only a part of the angles of the four-phase system are taken, for example, θ=0°, 9o°, and 270°.

Next, the reason why the digital signal transmission method of the present invention is strong against multipath distortion will be explained using an example.

In the following explanation, as an example of the transmission signal of the digital signal transmission method of the present invention, a two-phase transmission signal of θ=0°, 180'' as shown in FIG. 2 or 3 will be used. Furthermore, as a multipath model, a typical two-wave model will be considered.

Waves that are ahead in time are called direct waves, and waves that are delayed are called delayed waves.

In the digital signal transmission method of the present invention, detection is performed by delay detection using a delay line of n time slots. An example of the configuration of the detection circuit is shown in FIG.

However, in Fig. 5, 1 is an input terminal, 2 is a multiplier,
3 is an n time slot delayer, 4 is a low pass filter,
5 is a detection output terminal.

FIG. 6 is a diagram illustrating how a detection output signal becomes when these transmission signals are detected by the detection circuit of FIG. 5 under two-wave multipath. FIG. 6(a) shows the phase transition of an arbitrary time slot of the direct wave and a time slot n time slots after the arbitrary time slot. The magnitude of the phase transition within both time slots is equal and is denoted by φ. On the other hand, the phase transition of the delayed wave delayed by the propagation delay time difference τ, which cannot be ignored compared to the − time slot, is as shown in FIG. 6(b). The detection output at a certain point in time is the vector inner product of the combined phase of the two waves at that time and the combined phase of the two waves n time slots ago.

For example, in FIG. 6(C), the detection output in section B is the value of the vector inner product of the two-wave composite phase at time B'' and that at time B.

FIG. 7 illustrates the combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point A to E.

Note that the amplitude ratio of the direct wave and the delayed wave is ρ, and the phase difference is α. In addition, the phase axes in FIGS. 6(a) and 6(b) are
Although the positive direction may be leading or slow, it is assumed to be the leading direction. From FIG. 7, if the waveform is not deformed by the low-pass filter 4, or if the cutoff frequency is sufficiently high compared to the data transmission rate, the demodulated output at each time point A to E in FIG. 6(C) is as follows. become that way.

A... Undefined B... 1+ρ2+2ρcoSα...
・・・・■C・・・・・・ l+ρ2+2ρcos (
α±φ)・・・・・・■D ・・・・・・ 1+ρ2+
2ρcosα ・・・・・・■E ・・・・・・
In undefined intervals A and E, the values are undefined depending on the data values of the previous and subsequent time slots, respectively. Depending on the values of ρ and α, even if the detected signal in any one of sections B, D, and C becomes zero, the other does not become zero. Note that the superposition of equation 0 is 10 when the phase transition φ is slow, and 0 when the phase transition φ is fast.

For example, in FIG. 6 or FIG. 7, φ is phase leading, so in this case, the decoding of the 0 equation is -.

In reality, the cutoff frequency of the low-pass filter 4 is selected to be low enough to prevent code amount interference. Therefore, the detection output signal after passing through the low-pass filter 4 is as shown in FIG. 6(C).
The solid line waveform is filtered to form part of the eye pattern as shown by the dotted line in Figure 6 (C1).As mentioned above, sections B and D and section C produce complementary detection outputs. Therefore, the eye never closes.Furthermore, at least one of these valid detection outputs is never smaller than the invalid detection output in section A or E, so the fluctuation of the eye in the time axis direction is reduced. Therefore, there is little deterioration in the code error rate due to poor tracking of the reproduced clock.

As described above, the digital signal transmission method of the present invention is less susceptible to waveform distortion due to multipath due to a kind of diversity effect by combining different detection outputs of sections B and D and section C. Furthermore, since there are multiple types of values of φ, there are the same number of types of detection outputs in section C. Therefore, under specific multiplex conditions, for example φ1
Even if the error rate of a time slot with a phase transition of φ deteriorates, the error rate of a time slot with a phase transition φ other than φ does not necessarily deteriorate. In other words, burst errors are less likely to occur in the transmitted data string, and error correction can be simplified.

As described above, in a multipath transmission path, the bit error rate characteristics are significantly improved compared to the conventional method, and high-speed digital transmission becomes possible.

In addition, in this explanation, a two-phase system transmission signal such as θ=θ°, 180° as shown in Fig. 2 or 3 was used as an example, but transmission using other values of θ is also possible. For signals, the bit error rate characteristics can be significantly improved by using exactly the same principle.

For example, if θ is a multiphase system such as a four-phase system or an eight-phase system, the fifth
It is necessary to further connect a 90" phase shifter to the output of the 1-time slot delay device 3 shown in the figure, and perform delay detection on the orthogonal axis using this output signal as a reference signal. However, the configuration of the detection circuit becomes complicated. However, as explained above, the detection output of each detection axis has two types of effective detection outputs, and the bit error rate characteristics are significantly improved due to a kind of diversity effect by combining the two. .

There are only φ types of sets of these two types of effective detection outputs, and burst errors are reduced. T.

Regarding the ratio between BXC and T2, the lengths of sections BXC and D vary, but other than that, the explanation is exactly the same as above.

In other words, the digital signal transmission method of the present invention using a transmission signal that undergoes a phase transition as shown in FIG.
A kind of diversity effect by combining two different effective detection outputs regardless of the differences in the values of T t %φ, ..., θ, n, and
Due to the burst error reduction effect of having two or more types of valid detection output sets depending on the time slot, the bit error rate characteristics are significantly improved over the conventional method in multipath transmission paths, and high-speed digital transmission is possible. It becomes possible.

Effects of the Invention As described above, the present invention has one time slot phase transition of data, and the direction of the phase transition is either all leading or all lagging in each time slot, and the phase in any time slot is By using, as a transmission signal, a signal containing information to be transmitted in the phase difference between the transition and the first half and the second half of these two time slots, which are separated by a time slot, the conventional Enables faster digital transmission.

[Brief explanation of drawings]

Fig. 1 is a phase transition diagram of the transmission and transmission of the digital signal transmission method of the present invention, Figs. 2 to 4 are phase transition diagrams of an example of the transmission signal, and Fig. 5 is similar to Fig. 2 or 3. The configuration diagram of an example of a detection circuit corresponding to the transmission signal of the digital signal transmission method of the present invention as shown in FIGS. 6 and 7 explains that the digital signal transmission method of the present invention is resistant to multipath distortion. , a vector diagram showing the waveform diagram of the detection output signal and the composite phase of the multipath wave, Fig. 8 is a phase transition diagram of the transmission signal of the conventional digital signal transmission method, and Figs. 9 and 10 are the conventional digital signal transmission method. FIG. 2 is a vector diagram showing a waveform diagram of a detection output signal and a composite phase of multipath waves, explaining that the method is susceptible to multipath distortion. 1... Input terminal, 2... Multiplier, 3...
. . . n time slot delay device, 4 . . . low pass filter, 5 . . . detection output terminal. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2 Figure 3 J60'
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1clplElFigure 7C' 1σ data sequence -------/ 0
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Claims (7)

[Claims] (1) In a transmission device that transmits digital data, one time slot of data is divided into a first half and a second half at a predetermined ratio, and phase transitions of multiple types of angles are provided between the first half and the second half. , the direction of the phase transition is either all leading or all lagging in each time slot, and the phase transition in any given time slot and the phase transition in the time slot after that predetermined time slot are the same. A digital signal using a transmission signal having information transmitted in the phase difference between the first half and the second half of both time slots, which are equal in size and separated by the predetermined time slot. Transmission method. (2) The digital signal transmission method according to claim (1), wherein the predetermined ratio is 1:1. (3) The digital signal transmission method according to claim (1), wherein the predetermined ratio is not 1:1. (4) Claims (1) to (3) characterized in that the phase difference is either 0° or 180°.
The digital signal transmission method according to any one of paragraphs. (5) Claim (1) characterized in that the phase difference is any one of 0°, 90°, 180°, and 270°.
The digital signal transmission method according to any one of paragraphs to (3). (6) The digital signal transmission method according to any one of claims (1) to (3), wherein the phase difference is any angle obtained by dividing 360° into eight. (7) The digital signal transmission method according to any one of claims (1) to (3), wherein the phase difference is any angle obtained by dividing 360° into 16.